U.S. patent number 10,637,358 [Application Number 15/845,122] was granted by the patent office on 2020-04-28 for current control circuit.
This patent grant is currently assigned to Mosway Semiconductor Limited. The grantee listed for this patent is MOSWAY SEMICONDUCTOR LTD.. Invention is credited to Wan Tim Chan, Po Wa Chow, Shu Hung Henry Chung, Wing To Fan, Ka Wai Ho, Chiu Sing Tse, Chung Pui Tung.
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United States Patent |
10,637,358 |
Ho , et al. |
April 28, 2020 |
Current control circuit
Abstract
A current control circuit having a current regulation element, a
first control circuit, and a second control circuit. The first
control circuit is arranged to regulate, based on a reference
current, a current flowing with respect to the current regulation
element. The second control circuit is arranged to regulate, based
on a reference voltage, a voltage across the current regulation
element.
Inventors: |
Ho; Ka Wai (Hong Kong,
CN), Tung; Chung Pui (Hong Kong, CN), Chow;
Po Wa (Hong Kong, CN), Fan; Wing To (Hong Kong,
CN), Chan; Wan Tim (Hong Kong, CN), Chung;
Shu Hung Henry (Hong Kong, CN), Tse; Chiu Sing
(Hong Kong, CN) |
Applicant: |
Name |
City |
State |
Country |
Type |
MOSWAY SEMICONDUCTOR LTD. |
Hong Kong |
N/A |
CN |
|
|
Assignee: |
Mosway Semiconductor Limited
(Hong Kong, CN)
|
Family
ID: |
66816421 |
Appl.
No.: |
15/845,122 |
Filed: |
December 18, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190190389 A1 |
Jun 20, 2019 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03L
7/085 (20130101); G05F 3/24 (20130101); H03K
5/2481 (20130101); H03K 3/64 (20130101); H02M
1/08 (20130101); H02M 3/33515 (20130101); H03G
3/30 (20130101); H02M 3/33507 (20130101) |
Current International
Class: |
H02M
3/335 (20060101); H02M 1/08 (20060101); H03K
3/64 (20060101); H03K 5/24 (20060101); H03G
3/30 (20060101); H03L 7/085 (20060101); G05F
3/24 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Fureman; Jared
Assistant Examiner: Bukhari; Aqeel H
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
The invention claimed is:
1. A current control circuit comprising: a first current regulation
element; a first control circuit arranged to regulate, based on a
reference current, current flowing with respect to the first
current regulation element; and a second control circuit arranged
to regulate, based on a reference voltage, voltage across the first
current regulation element, wherein the first control circuit is
arranged to detect current passing the first current regulation
element, and compare the current detected with the reference
current for generation of a control signal, to substantially match
the current flowing with respect to the first current regulation
element to the reference current.
2. The current control circuit of claim 1, wherein the second
control circuit comprises a first voltage regulation element that
is controlled for regulating the voltage across the first current
regulation element.
3. The current control circuit of claim 2, wherein the first
voltage regulation element is connected in series with the first
current regulation element.
4. The current control circuit of claim 2, wherein, during
operation, when the voltage across the current control circuit is
larger than the reference voltage, voltage across the first current
regulation element is maintained to be substantially equal to the
reference voltage; and when the voltage across the current control
circuit is smaller than the reference voltage, the voltage across
the first voltage regulation element is substantially equal to
zero.
5. The current control circuit of claim 2, wherein the first
voltage regulation element is a series-pass device.
6. The current control circuit of claim 2, wherein the first
voltage regulation element is a transistor.
7. The current control circuit of claim 6, wherein the first
voltage regulation element is a MOSFET.
8. The current control circuit of claim 2, further comprising at
least one third control circuit arranged to regulate, based on a
respective reference voltage, voltage across the first current
regulation element, wherein each of the at least one third control
circuits includes a respective second voltage regulation element
that is correspondingly controlled for regulating the voltage
across the first current regulation element.
9. The current control circuit of claim 8, wherein at least one of
the second voltage regulation elements is connected in parallel
with the first voltage regulation element.
10. The current control circuit of claim 8, wherein at least one of
the second voltage regulation elements is connected in series with
the first voltage regulation element.
11. The current control circuit of claim 8, further comprising a
coordination-controller for controlling the reference voltage for
the second control circuit and the respective reference voltage for
each of the at least one third control circuits.
12. The current control circuit of claim 1, wherein the first
control circuit is further arranged to generate and provide the
control signal to the first current regulation element.
13. The current control circuit of claim 1, wherein the current
flowing with respect to the first current regulation element is a
current flowing into the first current regulation element.
14. The current control circuit of claim 1, wherein the current
flowing with respect to the first current regulation element is a
current flowing out of the first current regulation element.
15. The current control circuit of claim 1, wherein the first
current regulation element is a series-pass device.
16. The current control circuit of claim 1, wherein the first
current regulation element is a transistor.
17. The current control circuit of claim 16, wherein the first
current regulation element is a bipolar junction transistor.
18. The current control circuit of claim 1, further comprising: at
least one second current regulation element, wherein each second
current regulation element is arranged to be connected in parallel
with the first current regulation element; and at least one third
control circuit, wherein each third control circuit is associated
with a respective second current regulation element and is arranged
to regulate, based on a respective reference current, current
flowing with respect to the corresponding second current regulation
element.
19. The current control circuit of claim 18, further comprising a
coordination-controller for controlling the reference current for
the first control circuit and the respective reference current for
each of the at least one third control circuits.
20. The current control circuit of claim 1, wherein the second
control circuit is arranged to detect voltage across the first
current regulation element, and compare the voltage detected with
the reference voltage for generation of a control signal, to
substantially match the voltage across the first current regulation
element to the reference voltage.
21. A current control circuit comprising: a first current
regulation element; a first control circuit arranged to regulate,
based on a reference current, current flowing with respect to the
first current regulation element; and a second control circuit
arranged to regulate, based on a reference voltage, voltage across
the first current regulation element, wherein the second control
circuit comprises a first voltage regulation element that is
controlled for regulating the voltage across the first current
regulation element, and is arranged to detect voltage across the
first current regulation element, and compare the voltage detected
with the reference voltage for generation of a control signal, to
substantially match the voltage across the first current regulation
element to the reference voltage.
22. The current control circuit of claim 21, wherein the second
control circuit is further arranged to generate and provide the
control signal to the first voltage regulation element.
23. A current control circuit comprising: at least one current
regulation element; at least one first control circuit, wherein
each first control circuit is associated with a respective current
regulation element and arranged for regulating, based on a
respective reference current, current flowing with respect to the
corresponding current regulation element; and a plurality of second
control circuits, wherein each second control circuit has a voltage
regulation element, that is correspondingly controlled, for
regulating, based on a respective reference voltage, voltage across
the corresponding current regulation element, wherein the voltage
regulation elements are connected in parallel, or the voltage
regulation elements are connected in series, or some of the voltage
regulation elements are connected in parallel and some of the
voltage regulation elements are connected in series.
24. The current control circuit of claim 23, comprising a plurality
of current regulation elements connected in parallel and a
corresponding plurality of first control circuits.
25. The current control circuit of claim 24, further comprising a
coordination-controller for controlling the respective reference
currents for the plurality of first control circuits.
26. The current control circuit of claim 24 further comprising: a
first coordination-controller for controlling the respective
reference currents for the plurality of first control circuits; and
a second coordination-controller for controlling the respective
reference voltages for the plurality of second control
circuits.
27. The current control circuit of claim 26, wherein the first
coordination-controller and the second coordination-controller are
in a single controller.
28. A current control circuit comprising a plurality of current
control circuit modules, wherein each of the current control
circuit modules comprises a current control circuit of claim
26.
29. The current control circuit of claim 23, further comprising a
coordination-controller for controlling the respective reference
voltages for the plurality of second control circuits.
30. A current control circuit comprising: a first current
regulation element; a first control circuit arranged to regulate,
based on a reference current, current flowing with respect to the
first current regulation element; and a second control circuit
arranged to regulate, based on a reference voltage, voltage across
the first current regulation element, wherein the second control
circuit comprises a first voltage regulation element that is
controlled for regulating the voltage across the first current
regulation element, wherein, during operation, when the voltage
across the current control circuit is larger than the reference
voltage, voltage across the first current regulation element is
maintained to be substantially equal to the reference voltage; and
when the voltage across the current control circuit is smaller than
the reference voltage, the voltage across the first voltage
regulation element is substantially equal to zero.
Description
TECHNICAL FIELD
The invention relates to a current control circuit arranged to
regulate current transfer between a source and a load.
BACKGROUND
Current control circuits are generally arranged between a current
source and a load for regulating current flow, either
unidirectional current flow from the source to the load or
bi-directional current flow between the source and the load.
Some existing current control circuits operate as a current source
between the source and the load. However, these current sources are
not ideal because they have finite internal impedance, and may not
be able to maintain their respective current independently of a
voltage applied across it. In high voltage applications, these
current sources may not be able to deliver current with wide
bandwidth.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, there is
provided a current control circuit, comprising: a current
regulation element; a first control circuit arranged to regulate,
based on a reference current, a current passing the current
regulation element; and a second control circuit arranged to
regulate, based on a reference voltage, a voltage across the
current regulation element. In one embodiment of the first aspect,
the current control circuit may act as a current source. The
current control circuit is particularly adapted for regulating
current transfer between a source and a load, and for high-voltage
applications.
The reference current may be provided by a voltage signal or a
current signal indicative of a reference current value. The
reference current may be fixed or adjustable.
The reference voltage may be provided by a voltage signal or a
current signal indicative of a reference voltage value. The
reference voltage may be fixed or adjustable.
Preferably, the second control circuit comprises a voltage
regulation element that is controlled for regulating the voltage
across the current regulation element. The voltage regulation
element and the current regulation element are preferably connected
in series.
Preferably, the current control circuit is regulated such that
during operation when the voltage across the current control
circuit is larger than the reference voltage, the voltage across
the current regulation element is maintained to be substantially
equal to the reference voltage; and when the voltage across the
current control circuit is smaller than the reference voltage, the
voltage across the voltage regulation element is substantially
equal to zero.
Preferably, the first control circuit is arranged to: detect
current passing the current regulation element; and compare the
detected current with the reference current for generation of a
control signal, to substantially match the current passing the
current regulation element to the reference current. The first
control circuit may be further arranged to: generate and provide
the control signal to the current regulation element.
Preferably, the second control circuit is arranged to: detect
voltage across the current regulation element; and compare the
detected voltage with the reference voltage for generation of a
control signal, to substantially match the voltage across the
current regulation element to the reference voltage. The second
control circuit may be further arranged to: generate and provide
the control signal to the voltage regulation element.
The current passing the current regulation element may be a current
passing into the current regulation element, or alternatively, a
current passing out of the current regulation element.
In a preferred embodiment of the first aspect, the current
regulation element is a low-voltage current regulation element.
Preferably, the current regulation element is a series-pass device.
More preferably, the current regulation element is a transistor. In
one embodiment of the first aspect, the current regulation element
is a bipolar junction transistor, for example, a low-voltage
bipolar junction transistor.
Preferably, the voltage regulation element is a series-pass device.
More preferably, the voltage regulation element is a transistor. In
one embodiment of the first aspect, the voltage regulation element
is a MOSFET or a bipolar junction transistor. Preferably, the
voltage regulation element is not part of a switched-mode power
converter.
Preferably, the current control circuit further comprises: at least
one further current regulation element, each arranged to be
connected in parallel with the current regulation element; and at
least one further first control circuit, each associated with a
respective further current regulation element and being arranged to
regulate, based on a respective reference current, a current
passing the corresponding further current regulation element. The
reference current(s) for the further first control circuit(s) need
not be the same as the reference current for the first control
circuit. Likewise, the reference currents for different further
first control circuits need not be the same. Each of the reference
current may be provided by a voltage signal or a current signal
indicative of a corresponding reference current value. The
reference currents may be fixed or adjustable.
In a preferred embodiment of the first aspect, the further current
regulation element is a low-voltage current regulation element.
Preferably, the further current regulation element is a series-pass
device. More preferably, the further current regulation element is
a transistor. In one embodiment of the first aspect, the further
current regulation element is a bipolar junction transistor, for
example, a low-voltage bipolar junction transistor.
Preferably, the current control circuit further comprises: a first
coordination-controller for controlling the reference current for
the first control circuit and the respective reference current for
each of the at least one further first control circuit.
Preferably, the current control circuit further comprises: at least
one further second control circuit arranged to regulate, based on a
respective reference voltage, a voltage across the current
regulation element; each of the at least one further second control
circuit includes a respective further voltage regulation element
that is correspondingly controlled for regulating the voltage
across the current regulation element. The reference voltage(s) for
the further second control circuit(s) need not be the same as the
reference voltage for the second control circuit. Likewise, the
reference voltages for different further first control circuits
need not be the same. Each of the reference voltage may be provided
by a voltage signal or a current signal indicative of a
corresponding reference voltage value. The reference voltages may
be fixed or adjustable.
Preferably, each of the further voltage regulation elements is a
series-pass device. More preferably, the further voltage regulation
element is a transistor. In one embodiment of the first aspect, the
further voltage regulation element is a MOSFET or bipolar junction
transistor. Preferably, the further voltage regulation element is
not part of a switched-mode power converter.
In one embodiment of the first aspect, at least one of the further
voltage regulation elements may be connected in parallel with the
voltage regulation element. In another embodiment of the first
aspect, at least one of the further voltage regulation elements may
be connected in series with the voltage regulation element.
Preferably, the current control circuit further comprises: a second
coordination-controller for controlling the reference voltage for
the second control circuit and the respective reference voltage for
each of the at least one further second control circuit.
The first and second coordination-controllers may be separate
controllers, or they may be integrated as a single controller.
In accordance with a second aspect of the invention, there is
provided a current control circuit, comprising: at least one
current regulation element; at least one first control circuit,
each associated with a respective current regulation element and
arranged for regulating, based on a respective reference current, a
current passing the corresponding current regulation element; and
at least one second control circuit, each having a voltage
regulation element that is correspondingly controlled, for
regulating, based on a respective reference voltage, a voltage
across the at least one current regulation element. In one
embodiment of the second aspect, the current control circuit may
act as a current source. The current control circuit is
particularly adapted for regulating current transfer between a
source and a load, and for high-voltage applications.
The at least one current regulation element may be the current
regulation element and the further current regulation element(s) of
the first aspect. The at least one first control circuit may be the
first control circuit and the further first control circuit(s) of
the first aspect. The at least one voltage regulation element may
be the voltage regulation element and the further voltage
regulation element (s) of the first aspect. The at least one second
control circuit may be the second control circuit and the further
second control circuit (s) of the first aspect.
Preferably, the current control circuit comprises a plurality of
current regulation elements connected in parallel, and a
corresponding plurality of first control circuits.
Preferably, the current control circuit further comprises a first
coordination-controller for controlling the respective reference
current for the plurality of first control circuits.
Preferably, the current control circuit comprises a plurality of
second control circuits, wherein the voltage regulation elements
are connected: in parallel; in series; or at least some in parallel
and at least some in series. In one embodiment of the second
aspect, the voltage regulation elements may be arranged in an
array, with some connected in series and some connected in
parallel. The current control circuit may form a current control
circuit module.
Preferably, the current control circuit further comprises a second
coordination-controller for controlling the respective reference
voltage for the plurality of second control circuits.
The first and the second coordination-controllers may be separate
controllers, or they may be integrated as a single controller.
In accordance with a third aspect of the invention, there is
provided a current control circuit comprising a plurality of
current control circuit modules of the second aspect.
In accordance with a fourth aspect of the invention, there is
provided a power factor correction circuit including the current
control circuit of the first aspect.
In accordance with a fifth aspect of the invention, there is
provided a power factor correction circuit including the current
control circuit of the second aspect.
In accordance with a sixth aspect of the invention, there is
provided a power factor correction circuit including the current
control circuit of the third aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of
example, with reference to the accompanying drawings in which:
FIG. 1 is a circuit diagram of an exemplary current source;
FIG. 2A is a graph showing transfer characteristics of an existing
low-voltage bipolar junction transistor (Model no.:
MJD44H11TA9);
FIG. 2B is a graph showing transfer characteristics of an existing
high-voltage bipolar junction transistor (Model no.: TIP50G);
FIG. 3 is a circuit diagram showing a current control circuit in
one embodiment of the invention;
FIG. 4 is a circuit diagram showing an implementation of the
current control circuit of FIG. 3;
FIG. 5 is a circuit diagram showing a current control circuit in
another embodiment of the invention;
FIG. 6 is a circuit diagram showing a current control circuit in
yet another embodiment of the invention;
FIG. 7 is a circuit diagram showing a power factor correction
circuit;
FIG. 8 is a plot showing the key waveforms in the circuit of FIG.
7;
FIG. 9 is a is a circuit diagram showing a power factor correction
circuit incorporating a current control circuit in one embodiment
of the invention;
FIG. 10 is a plot showing the key waveforms in the circuit of FIG.
9;
FIG. 11A is a graph showing start-up transient waveforms in the
circuit of FIG. 9; and
FIG. 11B is a graph showing steady-state waveforms in the circuit
of FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows a current source 100 including a single bipolar
junction transistor T.sub.c connected in series with a resistor
R.sub.c, between nodes v.sub.a, and v.sub.b. The bipolar junction
transistor T.sub.c has a collector-emitter voltage of v.sub.Tc.
When the operating point of the bipolar junction transistor T.sub.c
is biased in the linear region, the collector current i.sub.c is
determined by the base current i.sub.b. In this linear region, an
approximation of the transfer characteristic between the collector
current i.sub.c and the base current i.sub.b is
.beta..times. ##EQU00001## where .beta. is the current gain. The
relationship may also be applicable to other transistors. Equation
(1) suggests that the collector current i.sub.c is linearly
proportional to the base current i.sub.b. However, this may not be
the case in practice because the current gain .beta. of transistors
may vary under the influence of various intrinsic and extrinsic
factors. Generally, the transfer characteristic of low-voltage
transistor devices exhibits a more linear behavior (as equation
(1)) when compared to that of high-voltage transistor devices.
FIGS. 2A and 2B show the transfer characteristics of an existing
low-voltage bipolar junction transistor (Model no.: MJD44H11TA9)
and an existing high-voltage bipolar junction transistor (Model
no.: TIP50G). As illustrated in FIG. 2A, for a given base current
i.sub.b, the collector current i.sub.c of the low-voltage bipolar
junction transistor is substantially constant over the operating
range of the collector-emitter voltage v.sub.ce. However, as
illustrated in FIG. 2B, the collector current i.sub.c of the
high-voltage bipolar junction transistor gradually increases with
the collector-emitter voltage v.sub.ce. Such characteristics imply
that the equivalent output impedance of high-voltage bipolar
junction transistors is much smaller than that of low-voltage
bipolar junction transistors.
One way to address this problem particularly prominent to
high-voltage bipolar junction transistors is to introduce a
feedback control mechanism to regulate the collector current
i.sub.c, for example, by sensing the collector current i.sub.c then
adjusting the base current i.sub.b. However, the bandwidth of the
frequency response of high-voltage transistor devices is narrow. As
a result, current control circuits with such high-voltage
transistor devices cannot deliver regulated current of wide
bandwidth.
FIG. 3 shows a current control circuit 300 in one embodiment of the
invention. The current control circuit 300 is particularly adapted
for high-voltage applications. The current control circuit 300
includes a series-pass structure T.sub.c arranged to act as a
current regulation element.
A first control circuit is arranged to regulate the current passing
into or out of the series-pass structure T.sub.c. The first control
circuit includes a detector 302 arranged to detect current passing
the series-pass structure T.sub.c, a comparator 304 for comparing
the detected current (in the form of a voltage signal
v.sub.ic,sense) with a reference current (in the form of a voltage
signal v.sub.ic,ref), and a controller 306 for generating and
providing a control signal to the series-pass structure T.sub.c to
substantially match the current passing the series-pass structure
T.sub.c to the reference current. In some other embodiments, the
detector 302, comparator 304, and controller 306 may be implemented
in one or more controllers.
A second control circuit is arranged to regulate the voltage across
the series-pass structure T.sub.c. The second control circuit
includes a series-pass structure T.sub.v arranged to operate as a
voltage regulation element, connected in series with the
series-pass structure T.sub.c. The two series pass structures
T.sub.v and T.sub.c are arranged between nodes v.sub.a and v.sub.b.
The second control circuit also includes a voltage sensor 308, in
the form of an operational amplifier, for detecting voltage across
series-pass structure T.sub.c, a comparator 310 for comparing the
detected voltage (in the form of a voltage signal v.sub.Tc,sense)
with a reference voltage (in the form of a voltage signal
v.sub.Tc,ref), and a controller 312 for generating and providing a
control signal to control the series-pass structure T.sub.v and
hence to substantially match the voltage v.sub.Tc across the
series-pass structure T.sub.c to the reference voltage. During
operation, the voltage v.sub.Tc across the series-pass structure
T.sub.c may be substantially equal to the reference voltage signal
v.sub.Tc,ref. In other words, at any moment in the time, the
voltage v.sub.Tc across the series-pass structure T.sub.c may be
slightly larger than or slightly smaller than the reference voltage
signal v.sub.Tc,ref. In some other embodiments, the sensor 308,
comparator 310, and controller 312 may be implemented in one or
more controllers.
In FIG. 3, the series-pass structure T.sub.c and the first control
circuit are collectively referred to as a current regulator A,
while the second control circuit is referred to as a voltage
regulator B. In the present embodiment, the current regulator A is
implemented with low-voltage series-pass devices. The control
circuit in the current regulator A is arranged to regulate the
current through the series-pass structure T.sub.c with relatively
wide frequency bandwidth. The voltage regulator B is used to
regulate the voltage across the series-pass structure T.sub.c. In
operation, a voltage across the series-pass structure T.sub.v may
be larger than a voltage across the series-pass structure T.sub.c.
In one embodiment, when the voltage across the current control
circuit is larger than the reference voltage v.sub.Tc,ref, the
voltage across the current regulation element is maintained to be
substantially equal to the reference voltage v.sub.Tc,ref, and when
the voltage across the current control circuit is smaller than the
reference voltage v.sub.Tc,ref, the voltage across the voltage
regulation element is substantially equal to zero.
FIG. 4 shows an implementation of the circuit 300 of FIG. 3. As
shown in FIG. 4, the series-pass structure T.sub.c and the
series-pass structure T.sub.v in the circuit 400 are bipolar
junction transistors.
Similar to the circuit 300 in FIG. 3, in operation of the circuit
400 of FIG. 4, the bipolar junction transistor T.sub.c is the main
current control element. It is controlled by a sensor 402, a
comparator 404, and a controller 406, which respective sense a
current of the bipolar junction transistor T.sub.c, compare the
sensed current of the bipolar junction transistor T.sub.c with a
reference current I.sub.ref (in the form of a voltage signal
v.sub.ic,ref), and generate a corresponding driving signal to the
base of the bipolar junction transistor T.sub.c with an error
amplifier (not shown). If the current delivered by the bipolar
junction transistor T.sub.c is smaller than I.sub.ref, the
controller 406 will increase the current to the base of bipolar
junction transistor T.sub.c. If the current delivered by the
bipolar junction transistor T.sub.c is larger than I.sub.ref, the
controller 406 will decrease the current to the base of bipolar
junction transistor T.sub.c. In FIG. 4, the emitter current of
bipolar junction transistor T.sub.c is sensed for control. However,
in another embodiment, the collector current i.sub.c may be sensed
instead. In practice, the value of the emitter current is very
close to the value of the collector current i.sub.c as the base
current i.sub.b is significantly smaller than the collector current
i.sub.c.
The bipolar junction transistor T.sub.v is the main element in the
voltage regulator B for regulating the voltage across the bipolar
junction transistor T.sub.c. The bipolar junction transistor
T.sub.v is controlled by a sensor 408, a comparator 410, and a
controller 412, which respectively sense the collector-emitter
voltage of the bipolar junction transistor T.sub.c, compare it with
a reference voltage v.sub.ref (in the form of a voltage signal
v.sub.Tc,ref), and generate a driving signal to the base of bipolar
junction transistor T.sub.v with an error amplifier (not shown).
The bipolar junction transistor T.sub.v shares a large portion of
the voltage across the current control circuit 400. If the voltage
across the bipolar junction transistor T.sub.c, is higher than
v.sub.ref, the error amplifier will reduce the current to the base
of the bipolar junction transistor T.sub.v. If the voltage across
the bipolar junction transistor T.sub.c is lower than v.sub.ref,
the error amplifier will increase the current to the base of the
bipolar junction transistor T.sub.v.
FIG. 5 shows a current control circuit 500 in another embodiment of
the invention. The current control circuit 500 in FIG. 5 is
generally the same as the circuits 300, 400 of FIGS. 3 and 4,
expect that the voltage regulator B divided into sub-voltage
regulators and current regulator A divided into sub-current
regulators. The circuit 500 in FIG. 5 allows for use of low-voltage
and low-current devices for improved operation efficiency and
effectiveness.
As illustrated in FIG. 5, the current regulator A is realized by
paralleling P multiple current regulators, referred to as
sub-current regulators, of smaller current ratings. Each
sub-current regulator is controlled with a respective controller to
regulate its current at the assigned current reference. The current
reference I.sub.ref,1, I.sub.ref,2, . . . , I.sub.ref,P for the
sub-current regulators are controlled by a coordination controller.
One or more of these controllers may be implemented together on the
same controller. The parallel-connected structure provides current
sharing feature to the current flowing through the current
regulator A.
The voltage regulator B is realized by a matrix of M (rows).times.N
(columns) of low-voltage voltage regulators, referred to as
sub-voltage regulators. The sub-voltage regulators of the same row
are connected in parallel. That is, each row has N sub-voltage
regulators connected in parallel. M rows of sub-voltage regulators
are connected in series. Each sub-voltage regulator is controlled
with a respective controller to regulate its voltage at the
assigned voltage reference. The voltage references V.sub.ref1,1,
V.sub.ref1,2, . . . , V.sub.ref,M,N for the sub-voltage regulators
are generated by a coordinated controller. One or more of these
controllers may be implemented together on the same controller. For
the voltage regulator B, the parallel-connected structure provides
current sharing feature to the current flow through the voltage
regulator B, and the series-connected structure provide voltage
sharing feature to the voltage stress applied across the voltage
regulator B.
By implementing the series and parallel connected structures as
illustrated in FIG. 5, voltage and current control with different
magnitudes and frequencies can be distributed to different
sub-regulators, respectively, and so that the dynamic response of
the current control circuit 500 can be further improved.
FIG. 6 shows a current control circuit 600 in yet another
embodiment of the invention. The circuit 600 is formed by multiple
current control circuits 500A, 500B, 500C of like construction
(similar to current control circuit 500 of FIG. 5), connected in
parallel between the source and the load. A common controller
controls the operation of the different current control circuits
500A, 500B, 500C.
To verify the performance of the current control circuit 300 of the
above embodiment, a current control circuit is built and applied to
control the input current waveform of a power factor corrector
using flyback DC/DC converter.
FIG. 7 shows a power factor correction circuit without the use of
the current control circuit of the invention. As shown in FIG. 7, a
series-pass device T.sub.c is connected in series with the input of
the flyback converter. The voltage v.sub.Tc across the series-pass
device T.sub.c is regulated at a low level by changing the
switching frequency and duty cycle of the main switch in the
flyback DC/DC converter. By adjusting the control signal to the
series-pass device T.sub.c, the input current of the flyback power
factor corrector is profiled to be in phase with the supply voltage
for regulating the output voltage.
FIG. 8 shows the key waveforms for the supply voltage v.sub.s, the
input current i.sub.in, and the voltage v.sub.Tc across the
series-pass device T.sub.c in the circuit of FIG. 7. At the
starting point of each half line cycle, the input capacitor
C.sub.in connected across the flyback power factor corrector will
be charged up by the supply voltage v.sub.s, following the input
current i.sub.in. However, within that time, the value of the input
current i.sub.in is small. The increase of the voltage v.sub.in
across the capacitor C.sub.in could not timely follow the increase
of the supply voltage v.sub.s. Therefore, the voltage difference
between the supply voltage v.sub.s and the capacitor voltage
v.sub.in will be applied to the series-pass device T.sub.c.
Following the increase in the input current i.sub.in, the rising
speed of v.sub.in increases. The difference between the supply
voltage v.sub.s and the capacitor voltage v.sub.in is reduced.
Thus, the voltage v.sub.Tc, across the series-pass device T.sub.c
will back to the level equal to the reference voltage v.sub.ref. In
other words, voltage stress (voltage v.sub.Tc, across the
series-pass device T.sub.c) is particularly high when the input
current i.sub.in is low and the supply voltage v.sub.s is high. In
one example, when the input current is zero or close to zero, all
or substantially all voltage stress from supply side will be
applied across the series-pass device T.sub.c. In such case, a
low-voltage device cannot be used for high-voltage application.
FIG. 9 shows a power factor correction circuit incorporating a
current control circuit 900 in one embodiment of the invention. In
the current control circuit 900 of FIG. 9, the current regulation
element T.sub.c is implemented by using a bipolar junction
transistor, and voltage regulation element T.sub.v is implemented
by using a MOSFET. Operational amplifiers are used as the
controllers in the two control circuits. The operation of the
circuit 900 is generally the same as that described with reference
to FIGS. 3 and 4.
FIG. 10 shows the key waveforms for the input current i.sub.in, the
voltage at v.sub.a, and the voltage v.sub.Tc, across the bipolar
junction transistor T.sub.c in the circuit 900 of FIG. 9. As
illustrated, a large voltage fluctuation is present at the
beginning of every half line cycle. When the voltage fluctuation is
present across the circuit, most of the voltage will be dropped
across the MOSFET T.sub.v. Therefore, the input current i.sub.in
can be properly regulated and the bipolar junction transistor
T.sub.c can operate under low voltage stress.
FIGS. 11A and 11B are graphs showing start-up transient waveforms
and steady-state waveforms in the circuit 900 of FIG. 9. In the
tests, the supply voltage is 265V.sub.ac and the reference voltage
V.sub.ref is set to 5V. The waveforms show that the voltage across
the bipolar junction transistor T.sub.c, can be controlled to be
below 5V and the extra 150V are distributed to the MOSFET
T.sub.v.
The above embodiments of the invention provide respective current
control circuit that is arranged to effectively regulate current
between source and load. The current control circuits are
particularly adapted for high-voltage application, especially in
cases when low-voltage current regulation element is used. The
current control circuit may be connected in series between the load
and the source. In operation, the voltage across current regulation
element can be clamped when the voltage stress across exceeds a
reference value. Advantageously, the current control circuit can
operate under low and stable voltage stress so that low-voltage
current regulation element can be used in high-voltage
applications.
It will be appreciated by persons skilled in the art that numerous
variations and/or modifications may be made to the invention as
shown in the specific embodiments without departing from the spirit
or scope of the invention as broadly described. For example, the
current regulation element may be implemented using devices other
than series-pass devices. The current regulation element may be
implemented using transistors other than bipolar junction
transistors, or with any circuits or modules that is arranged to
operate as a current source. Likewise, the voltage regulation
element may be implemented using devices or circuits other than
series-pass devices. For example, the voltage regulation element
may be implemented using transistors other than MOSFETs or bipolar
junction transistors. The voltage across the voltage regulation
element can be equal to or smaller than the voltage across the
current regulation element. In embodiments with multiple voltage
regulation elements, these elements may be arranged solely in
series, solely in parallel, or in an array with both series and
parallel connections. More generally, the array may include any
number of rows and columns. The current control circuit may be used
in other circuits, not necessarily power factor correction
circuits. The present embodiments are, therefore, to be considered
in all respects as illustrative and not restrictive.
* * * * *